Since polypropylene shows excellent mechanical properties and moldability while it has low density, it is broadly used in various fields. However, it has inferior impact resistance and heat resistance so that, with the aim of overcoming such problems, various polypropylene resin compositions have been proposed in which an ethylene-propylene copolymer rubber, ethylene-butene copolymer rubber or the like rubber component and talc or the like inorganic filler are added to an ethylene-propylene block copolymer obtained by multi-stage polymerization.
For example, JP-A-1-149845 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a resin composition which comprises (a) 59 to 74% by weight of a propylene-ethylene block copolymer in which it contains 5 to 12% by weight of a boiling xylene-soluble component having an ethylene content of from 20 to 60% by weight, the ethylene content of the whole polymer is from 1 to 7% by weight and it has a melt flow rate of from 15 to 50 g/10 minutes, (b) 35 to 20% by weight of an ethylene-propylene copolymer rubber having a propylene content of from 20 to 60% by weight and a Mooney viscosity ML.sub.1+4 (100.degree. C.) of from 100 to 150 and (c) 3 to 6% by weight of talc having a specific surface area of 30,000 cm.sup.2 /g or more and an average particle size of from 0.5 to 2.0 .mu.m.
In the related polypropylene resin compositions, their impact resistance is improved generally by the addition of a rubber component and their rigidity is improved by the addition of an inorganic filler in general, so that their rigidity is sacrificed for improving impact resistance and their impact resistance is sacrificed for improving rigidity, thus entailing a relatively limited range of the use of each composition. For example, in the case of automobiles, a material having improved impact resistance is used in bumper and the like exterior parts, and a material having improved rigidity is used in instrumental panel and the like interior parts, because there are no polypropylene materials which can be used in both cases. In addition, with the advance in the thinning methods of molded products for the purpose of improving production efficiency and lightening of the products, more superior flow characteristics are in demand for such compositions.